The goal of the National Center for Simulation in Rehabilitation Research (NCSRR) is to equip the rehabilitation research community with state-of-the-art simulation tools, enabling investigators to complement experimental studies of human performance with advanced simulation software and biomechanical models. Users of this technology will focus on critical areas of medical rehabilitation, including stroke, spinal cord injury, cerebral palsy, rehabilitation robotics, prosthetics, osteoarthritis, and other areas. We propose the following specific aims: 1. Develop and disseminate the world's most advanced technology for simulation of musculoskeletal dynamics and accelerate its appropriate use in rehabilitation research. 2. Provide technical support to OpenSim users engaged in medical rehabilitation research. 3. Train 500 rehabilitation scientists in the use of simulations via intensive multiday workshops and introduce over 1000 movement scientists, rehabilitation specialists, physicians and surgeons to the strengths and limitations of musculoskeletal simulation. 4. Award grants to innovative and meritorious projects to accelerate the use of simulations in rehabilitation research and advance medical rehabilitation. 5. Build an international community of simulation experts to support the NCSRR mission. The development and dissemination of open software for the movement science and rehabilitation communities addresses a critical barrier to progress in the field. The software is designed in close partnershi with rehabilitation scientists and physicians to address critical, clinically motivated questions across the spectrum of medical rehabilitation. Over its first five years, the NCSRR has fostered a rapidly growing community of rehabilitation scientists who are actively engaged in this process. We have delivered our software to 18,000 users, trained over 900 researchers, and granted over 60 awards that have seeded larger independent grants and numerous publications. We will build on this momentum over the next five years, focusing our technology development, training efforts, and collaborative programs to meet the evolving needs of the rehabilitation research community.